Latching mechanism

ABSTRACT

The latching mechanism comprises a pivotable member that cooperates with a contact member for coupling the contact member to the pivotable member. A drive mechanism moves the contact member into contact with the pivotable member thereby pivoting the pivotable member and allowing the contact member to seat in the pivotable member. A biasing mechanism urges the pivotable member into its initial position. The drive mechanism can be also utilized to release the contact member from the pivotable member.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to copending United States PatentApplication Ser. No. 217,055 filed Dec. 16, 1980 in the name of L.Veronesi et al. entitled "Hydraulic Drive Mechanism" and is assigned tothe Westinghouse Electric Corporation.

BACKGROUND OF THE INVENTION

This invention relates to latching mechanisms and more particularly tolatching mechanisms for latching reactivity control mechanisms innuclear reactors.

As is well known in the art, a nuclear power plant generates electricityfrom heat produced by fissioning of nuclear material. The nuclearmaterial is contained within fuel assemblies which comprise the core ofa nuclear reactor. As the reactor coolant is circulated through thenuclear reactor core heat is transferred from the core to the reactorcoolant which is then conducted to a remote location for generatingsteam and electricity in a conventional manner.

Control of the nuclear reactor is usually achieved by control rods whichare dispersed throughout the nuclear reactor core and are mounted formovement into and out of the core. The control rods function byabsorbing excess neutrons produced by the nuclear reaction. In additionto control rods, a nuclear reactor may also have displacer rods disposedtherein which are also mounted for movement into and out of the core toeffect reactivity of the core as described in copending U.S. Patentapplication Ser. No. 217,060 filed Dec. 16, 1980 in the name of W. J.Dollard et al. entitled "Mechanical Spectral Shift Reactor" and assignedto the Westinghouse Electric Corporation.

After a period of operation of a nuclear reactor, it is necessary to beable to access and replace the spent fuel assemblies in the reactor withfresh fuel assemblies. During this operation, it is necessary to removethe reactor vessel closure head so as to be able to access the fuelassemblies in the nuclear reactor core. Since the control rods anddisplacer rods are attached to their respective drive mechanisms whichare mounted on the reactor vessel closure head, it is expedient todisconnect the control rods and displacer rods from their correspondingdrive mechanisms before removing the reactor vessel closure head whilemaintaining the control rods and displacer rods in the nuclear reactorcore.

The ability of leaving the control rods and displacer rods in thenuclear reactor core during refueling may be achieved by providing adisconnect mechanism between the control rod and the control rod drivemechanism. One such disconnect mechanism is disclosed in U.S. Pat. No.4,147,589, entitled "Control Rod for a Nuclear Reactor", issued April 3,1979 in the name of W. G. Roman et al. and assigned to the WestinghouseElectric Corporation. In the patent to Roman et al., there is describeda control rod assembly for a nuclear reactor having a remotelydisengageable coupling between the control rod and the control rod driveshaft. The coupling is actuated by first lowering then raising the driveshaft. The described motion causes actual repositioning of a pin in agrooved rotatable cylinder, each being attached to different parts ofthe drive shaft which are axially movable relative to each other. Whilethe patent to Roman et al. describes one mechanism for disconnecting adrive mechanism from a reactivity control mechanism in a nuclearreactor, there is needed an alternative and simple mechanism foreffecting such a disconnection.

SUMMARY OF THE INVENTION

The latching mechanism comprises a pivotable member that cooperates witha contact member for coupling the contact member to the pivotablemember. A drive mechanism moves the contact member into contact with thepivotable member thereby pivoting the pivotable member and allowing thecontact member to seat in the pivotable member. A biasing mechanismurges the pivotable member into its initial position. The drivemechanism can be also utilized to release the contact member from thepivotable member.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming the subject matter of the invention, it isbelieved the invention will be better understood from the followingdescription, taken in conjunction with the accompanying drawings,wherein:

FIG. 1 is a partial cross-sectional view in elevation of a nuclearreactor;

FIG. 2 is a cross-sectional view in elevation of the top portion of thenuclear reactor;

FIG. 3 is a cross-sectional view in elevation of the drive mechanism;

FIG. 4 is a view along line IV-IV of FIG. 3;

FIG. 5 is an exploded view in perspective of the latching mechanism;

FIG. 6 is a cross-sectional view of the latching mechanism;

FIG. 7 is a cross-sectional view of the latching mechanism; and

FIGS. 8-11 are cross-sectional views in elevation of the latchingmechanism showing the steps of the latching procedure.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

During the refueling of nuclear reactors, it is advantageous todisconnect rod drive mechanisms from the drive rods when the reactorvessel closure head is removed for refueling. In order to accomplishthis, it is necessary to have a disconnect mechanism between the roddrive mechanisms and the drive rod. The invention described hereinprovides a means for latching reactivity control rods in a nuclearreactor while allowing the drive rod to be disconnected from the drivemechanism during the refueling process.

Referring to FIGS. 1 and 2, the nuclear reactor is referred to generallyas 10 and comprises a reactor vessel 12 having a removable closure head14 attached to the top thereof by means of bolts 16. A plurality of fuelassemblies 18 are disposed within reactor vessel 12 and comprise reactorcore 20. A plurality of control rod drive mechanisms 22 which may be ofthe type generally used in the art are mounted on and extend throughclosure head 14 for inserting and removing control rods (not shown) fromfuel assemblies 18 as is well understood in the art.

Still referring to FIGS. 1 and 2, a plurality of displacer rod drivemechanisms 24 are also attached to and extend through closure head 14. Aplate 26 is suspended from the inside of closure head 14 by supports 28.A multiplicity of funnel-shaped guide members 30 are attached to plate26 and are arranged in line with each of the control rod drivemechanisms 22 and displacer rod drive mechanisms 24. Each guide member30 has a hole therethrough that allows a drive rod 32 to be slidablydisposed therein. Each drive rod 32 is either attached at its lower endto a cluster of displacer rods 34 and capable of being attached at itsupper end to a displacer rod drive mechanism 24 or attached at its lowerend to a cluster of control rods (not shown) and at its upper end to acontrol rod drive mechanism 22. The arrangement of control rods anddisplacer rods may be such as that described in copending U.S. Patentapplication Ser. No. 217,060 filed Dec. 16, 1980 in the name of W. J.Dollard et al. entitled "Mechanical Spectral Shift Reactor". Each driverod 32 whether attached to a control rod drive mechanism 22 or adisplacer rod drive mechanism 24, is capable of being disengaged fromeither its respective displacer rod drive mechanism 24 or control roddrive mechanism 22 so that closure head 14 may be removed carrying withit the control rod drive mechanisms 22, displacer rod drive mechanism 24and plate 26 with guide members 30 attached thereto. Closure head 14 maybe removed during the refueling process to replace spent fuel assemblies18 with fresh ones. The disconnectability of drive rod 32 from itsrespective drive mechanism enables this to be easily accomplished. Whenit is time to replace closure head 14, guide members 30 aid in aligningeach drive rod 32 with its respective drive mechanism so that whenclosure head 14 is placed on reactor vessel 12, each drive rod 32 slidesthrough its respective guide member 30 and into its respective drivemechanism.

Referring now to FIG. 3, displacer rod drive mechanism 24 comprises asubstantially cylindrical metal housing 36 which is welded to andextends through closure head 14. Housing 36 has a cap 38 attached to thetop thereof which has a channel 40 therethrough that is connected toconduit 42. Conduit 42 is connected to cap 38 and to a tank (not shown)12 and has a flow regulating valve 44 disposed therein. Since theinterior of housing 36 is exposed to the interior of reactor vessel 12,the reactor coolant fills the void spaces within housing 36 and flowsthrough conduit 42 when valve 44 is open. A bearing housing 46 isremovably disposed within housing 36 and has a plurality of first pistonrings 48 attached to the outside thereof near its lower end which extendinto contact with the inside of housing 36 for aligning bearing housing46 within housing 36 but allowing for the removal of bearing housing 46.Drive rod 32 is slidably disposed within bearing housing 46 in a mannerso as to be able to be moved axially with respect to bearing housing 46and housing 36 under the influence of the reactor coolant pressure. Aplurality of second piston rings 50 which may be Inconel are removablydisposed within bearing housing 46 so as to be able to contact drive rod32. Second piston rings 50 provide a mechanism for allowing drive rod 32to slide within bearing housing 46 while limiting the flow of reactorcoolant through bearing housing 46 and housing 36 when valve 44 is open.In this manner, the movement of drive rod 32 can be controlled byopening and closing valve 44. Second piston rings 50 are arranged sothat they may be replaced when bearing housing 46 is removed fromhousing 36.

Referring now to FIGS. 3 and 4, a plurality of roller bearings 52 aredisposed on a like number of axles 54 in a manner so as to allow theouter surface of roller bearings 52 to contact the outer surface ofdrive rod 32 while allowing the rotation of roller bearings 52. As shownin FIG. 4, four roller bearings 52 may be used so as to align drive rod32 within bearing housing 46 while aiding in the movement of drive rod32. A plurality of screws 56 corresponding to the number of rollerbearings 52 are used to attach holding member 58 to bearing housing 46so as to hold roller bearings 52 within bearing housing 46 yet allowreplacement thereof by removal of screws 56 and holding member 58. In alike manner, a second set of roller bearings 60 are disposed at theother end of bearing housing 46 to provide alignment of drive rod 32.

Referring again to FIG. 3, drive rod 32 has a flexible rod 62 attachedto the top end thereof which may be an Inconel rod. Flexible rod 62 hasa spear-shaped member 64 attached to the top end of it. A hollowcylindrical divider 66 is attached to the lower end of cap 38 and incolinear alignment with channel 40. Divider 66 defines at least threechambers in the bottom end of cap 38 such as first chamber 68 and secondchamber 70 that are of the size to accommodate spear 64.

Referring now to FIGS. 3, 5, 6 and 7, a latching mechanism 72 isdisposed within housing 36 and adjacent to first chamber 68 and secondchamber 70 and comprises a metal pivotable member 74 having a first slot76 extending the entire length of one side. First slot 76 is of the sizesmall enough to prevent spear 64 from passing therethrough but of a sizelarge enough to allow flexible rod 62 to pass therethrough. Pivotalmember 74 also has a first bore 78 and a second bore 80 in the top endthereof with first bore 78 capable of being aligned with first chamber68 ad second bore 80 capable of being aligned with second chamber 70when pivotal member 74 is properly pivoted. First bore 78 extends tonear the bottom of pivotal member 74 and has a ledge 82 at its lowerend. Whereas, second bore 80 extends the entire length of pivotal member74. A second slot 84 is defined between first bore 78 and second bore 80which also is of a size small enough to prevent spear 64 from passingthroughout but of a size large enough to allow flexible rod 62 to passtherethrough. Two pins 86 each having one end rotatably disposed withinpivotal member 74 and each having their other end rotatably disposedwithin housing 36 allow pivotal member 74 to pivot within and relativeto housing 36 as shown in FIG. 6. A plurality of biasing means 88 whichmay be coil springs, are disposed around each pin 86 and are attached atone end to housing 36 and at the other end to pivotal member 74 forurging pivotal member 74 into a position as shown in FIG. 3. Biasingmeans 88 are chosen such that they are capable of pivoting pivotalmember 74 in a manner such that the top end of slot 76 contacts theinside of housing 36. However, biasing means 88 are chosen such thatwhen spear 64 contacts and moves along first slot 76 as shown in FIG. 5,spear 64 can pivot pivotal member 74 in a manner so as to allow spear 64to slide into first chamber 68.

Referring now to FIGS. 8-11, when it is desired to raise drive rod 32thereby raising displacer rods 34 or other similar devices, valve 44 isopened which allows the pressure in the upper end of housing 36 to dropto about 1950 psi and which allows the reactor coolant inside reactorvessel 12 to exert a force on drive rod 32, which causes drive rod 32 tomove upwardly toward cap 38. Since the pressure in reactor vessel 12 isnormally about 2250 psi, this pressure acting on the lower end of driverod 32 creates a force of approximately 700 lbs. on drive rod 32 whichcauses the lifting action. Since second piston rings 50 create arelatively tight seal between drive rod 32 and bearing housing 46, driverod 32 is raised at a slow rate with respect to bearing housing 46. Forexample, under a force of approximately 700 lbs., drive rod 32 will riseat a rate of approximately 1 ft/sec. This slow rate of rise, eliminatesthe need to have a slowing mechanism such as a fluid dashpot attached toor associated with drive rod 32 to slow its rise. The relatively tightseal of second piston rings 50 with drive rod 32 also limits the amountof reactor coolant that passes therebetween so that adjusting valve 44can effectively control the rate of movement of drive rod 32. As driverod 32 rises, spear 64 contacts first slot 76 and rides therealong asshown in FIG. 5. Spear 64 exerts a force on pivotal member 74 so as topivot pivotal member 74 when spear 64 passes the location of pins 86.This pivoting motion allows spear 64 to pass beyond pivotal member 74and into first chamber 68 as shown in FIG. 8. As spear 64 passes pivotalmember 74, flexible rod 62 passes through first slot 76 and into firstbore 78. As flexible rod 62 passes into first bore 78, pivotal member 74is pivoted back into its original position under the action of biasingmeans 88 as shown in FIG. 8. Next, valve 44 is closed and the weight ofdrive rod 32 and the members attached thereto cause drive rod 32 toslowly slide downwardly within bearing housing 46 such that spear 64enters first bore 78 as shown in phantom in FIG. 8. As spear 64continues downwardly into first bore 78, it causes pivotal member 74 topivot into a position as shown in FIG. 9. The downward slide of driverod 32 and spear 64 is halted when spear 64 reaches ledge 82 at thebottom of first bore 78. Ledge 82 at the bottom first bore 78 holdsspear 64 therein. When in this position as shown in FIG. 9, pivotalmember 74 has been pivoted such that first bore 78 is in alignment withsecond chamber 70. Also, when in the position as shown in FIG. 9, spear64 and drive rod 32 are in the raised position with displacer rods 34fully withdrawn from core 20. Also, when in this position, drive rod 32is locked in the up position. This position may be maintained as long asit is desired to have displacer rods 34 out of core 20.

Referring now to FIGS. 9-11, when it is desired to lower displacer rods34 into core 20, valve 44 is again opened which allows reactor coolantto flow through housing 36, channel 40, and conduit 42. This allowsdrive rod 32 to again rise with respect to housing 36. As drive rod 32rises, spear 64 rises into second chamber 70. When spear 64 has riseninto second chamber 70, spear 64 contacts cap 38 which prevents furtherrise of drive rod 32 as shown in FIG. 10. Once again, when spear 64 haspassed beyond pivotal member 74, pivotal member 74 is pivoted intocontact with housing 36 and flexible rod 62 extends through second slot84 as shown in FIG. 10. Next, valve 44 can be closed which allows thepressure on both ends of drive rod 32 to reach the same level. Once thepressure has thus reached the same level, the weight of drive rod 32 andmechanisms attached thereto, cause drive rod 32 to slowly movedownwardly with respect to housing 36. As drive rod 32 moves downwardly,spear 64 enters second bore 80 as shown in FIG. 10 in phantom. As spear64 passes through second bore 80, it exerts a force on pivotal member 74which causes pivotal member 74 to pivot into a position as shown in FIG.11. Since second bore 80 extends through the entire length of pivotalmember 74, the downward slide of spear 64 is not halted. Rather, spear64 and drive rod 32 continue to fall through bearing housing 46 untildisplacer rods 34 have reached their maximum low position, thus fullyinserting displacer rods 34 in core 20. Therefore, it can be seen thatlatching mechanism provides a mechanism by which a member can be held inan upper or lower position by moving the member with respect to thelatching mechanism.

I claim:
 1. A latching mechanism comprising:a mounting member; apivotable member pivotably attached to said mounting member having afirst bore and a second bore therein and having a first slot, a firstbore, and a second slot therein with each extending from the top to thebottom ends of said pivotable member with said first slot being definedalong one edge of said pivotable member and extending into said firstbore, with said first bore being defined adjacent to and substantiallyparallel with but not in colinear alignment with said first slot andhaving a ledge therein, and with said second slot being defined alongthe length of said first bore and extending into said first bore;biasing means attached to said pivotable member for pivoting saidpivotable member relative to said mounting member; a contact memberhaving a head on one end thereof with said head being capable of passinginto said first bore and not being capable of passing through said firstslot and said second slot, with said contact member being capable ofbeing inserted through said first slot, said first bore, and said secondslot and with said head being capable of being captured by said ledge insaid first bore; and drive means connected to said contact member formoving said head into contact with said pivotable member therebypivoting said pivotable member relative to said mounting member therebyallowing said head to be inserted in said first bore while said contactmember passes through said first slot thus latching said contact memberto said pivotable member.
 2. The latching mechanism according to claim 1wherein said pivotable member has a second bore therein extending fromthe top to the bottom end thereof for allowing said contact member andsaid head to pass therethrough thereby disconnecting said contact memberfrom said pivotable member.
 3. The latching mechanism according to claim2 wherein said second bore is defined adjacent to and substantiallyparallel with but not in colinear alignment with said first bore andextends along the length of said second slot.
 4. The latching mechanismaccording to claim 3 wherein said contact member is a flexible rod. 5.The latching mechanism according to claim 4 wherein said head is aspear-shaped member.
 6. The latching mechanism according to claim 5wherein said biasing means comprises a coil spring attached to saidpivotable member and to said mounting member for pivoting said pivotablemember.
 7. The latching mechanism according to claim 6 wherein saidmounting member comprises a housing wherein said pivotable member isdisposed.